Current widely used devices use principles where the interactions and/or identification with a computer or a mobile phone, a wearable or any other kind of device are performed by user actions—buttons, touchscreens, gestures, voice commands, NFC identifications, biometric sensors (like a fingerprint or face detection), pin codes, etc.
Sometimes, the interaction and/or identification is based on a radio signal strength indication (RSSI) from some other physical item—a mobile phone, a smartwatch or a special tag is used to unlock a workstation.
Example of prior art is Apple's WWDC16 feature called “auto unlock” and is using physical proximity as assumption of user presence. While it sounds perfect this is not secure. Computer can be brought to other side of thin wall to unsuspecting user wearing iWatch and malicious auto unlock feature may happen.
It is also common for many current devices to include some passive interactions based on sensor data, where the data is used to extrapolate the intention or desire of the user as well as the convenience of certain actions. Simple example could be the screen brightness control based on light sensor or the screen orientation based on ground detection. More sophisticated cases would be, for example, using activity tracking based on IMU sensors to control the volume of incoming calls depending on that activity, disconnect an alarm if the user is already awake and moving, unlocking a smartwatch screen when a looking-to-the-screen gesture is detected, etc. Often these technologies are combined for creating more trustful and sophisticated interactions and/or identification processes—for example, keyless entry to a car and starting it may require physical action to open the doors, but later just the proximity of a key tag is enough to start the engine. Prior art of keyless entry systems and problems are explained in Francillon, A. et al., Relay Attacks on Passive Keyless Entry and Start Systems in Modern Cars.
The known methods are too complicated processes, do not allow to identify the unauthorized use and don not work properly and therefore insecure.